1. Field of the Invention
The present invention relates to a controller, for controlling the revolving speed (number of revolutions) of a cooling fan, which is suitable for use in a cooling fan mounted in working machinery such as a hydraulic shovel.
2. Description of the Related Art
Working machines, such as a hydraulic shovel, are being used in urban areas and residential areas with ever-increasing frequency, so that machine noise during operation has become an important consideration. The generation of machine noise is greatly affected by the presence of a cooling fan that introduces the air as a cooling wind into cooling equipments such as an oil cooler and radiator.
Cooling fans are normally designed, taking a severe operating environment into account. For example, even when the air temperature is high such as 30° C. and an engine runs continuously in a condition of maximum load such as full throttle, the cooling ability of cooling equipments is raised by increasing the revolving speed of the cooling fan to admit a cooling wind at a higher volume into the cooling equipments so that the engine is not overheated.
However, if the revolving speed of the cooling fan is increased, the rotational resistance due to air will become great, and wind noise by revolution of the cooling fan will be increased. This will have a great influence on the generation of noise.
For noise reduction, it is preferable to make the revolving speed of cooling fans as low as possible except when necessary, such as high-load time, etc.
Because of this, a variety of techniques have been developed for controlling the revolving speed of a cooling fan.
For example, the revolving speed of a cooling fan is being controlled according to the temperature of hydraulic operating oil employed for the operation and travel of working machinery.
Furthermore, for example patent document 1, regarding construction machinery (working machinery), discloses a technique that controls the revolving speed of a cooling fan by a fan controller in accordance with the temperature (water temperature) Tw of engine-cooling water and the temperature (oil temperature) To of the hydraulic operating oil circulating through a hydraulic system.
More specifically, in the technique of the above patent document 1, the water temperature Tw is detected by a water-temperature sensor, and the oil temperature To is detected by an oil-temperature sensor. When the detected water temperature Tw and oil temperature To are lower than predetermined first temperature Tw1 and To1, the cooling fan is not operated.
When the water temperature Tw is between the first temperature Tw1 and a second temperature Tw2 higher than the first temperature Tw1 and the oil temperature To is lower than the first temperature To1, and when the water temperature Tw is lower than the first temperature Tw1 and the oil temperature To is between the first temperature To1 and a second temperature To2 higher than the first temperature To1, the cooling fan is operated at low speeds.
When the water temperature Tw and oil temperature To are between the first temperatures Tw1 and To1 and the second temperature Tw2 and To2, the cooling fan is operated at intermediate speeds.
When the water temperature Tw is higher than the second temperature Tw2 and the oil temperature To is between the first temperature To1 and the second temperature To2, when the water temperature Tw is between the first temperature Tw1 and the second temperature Tw2 and the oil temperature To is higher than the second temperature To2, and when the water temperature Tw and oil temperature To are higher than the second temperatures Tw2 and To2, the cooling fan is operated at high speeds.    Patent Document 1: Japanese Patent laid-open publication No. HEI 5-288053